Kevin,
I believe that when the multicast packet arrives at an interface the TTL in
the IP header is automatically decremented by 1.
This applies even if a threshold has been set.
If the TTL-threshold on an interface is set to a number which is higher than
the TTL in the multicast packet, then the packet will be dropped at that
interface.
Example: If my initial TTL value is 64, I can set a TTL threshold of 65 at
all the border routers and the multicast packets will never leave the
internal Net. The multicast packets will go from internal router to internal
router decrementing by 1 each time.
This makes sense to me because the multicast algorithm is probably a
separate module which says "subtract the TTL-threshold from the TTL value
and if the result is a positive integer, let the packet through, if not
discard the packet"
The result is to give some control as to how far the packets are allowed to
propagate without having to rewrite the IP module. The IP rule of
decrementing by 1 (sec or hop) remains intact.
I will do some IP multicasting tests soon to see if the above makes sense.
The IOS has not failed to surprise me yet.....
Winston.
-----Original Message-----
From: Kevin Welch [mailto:[EMAIL PROTECTED]]
Sent: Thursday, December 28, 2000 8:44 AM
To: [EMAIL PROTECTED]
Subject: IP Multicasting TTL
I am boning up on IP multicasting and I have a question about TTL =
Thresholds. When a multicast packet passes through an interface with a =
configured TTL threshold, is the TTL decremented my 1 or by the =
threshold value?
-- Kevin=20
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